This invention relates generally to machine control methods and systems for machines having machine elements, such as for example construction machines such as graders, milling machines, pavers, and slip-forming machines. More particularly, the present invention relates to a machine control method and system using a stationary tracking station that determines the location and orientation of the machine element, and transmits this information to the machine for use in controlling the operation of the machine element.
It is desirable to monitor the position and movement of various types of relatively slow-moving machines, such as for example construction machinery including graders, pavers, and slip-forming, as well as the position, orientation and movement of machine elements associated with such machines. This information can then be used to control the operation of the monitored machines.
While in the past, machine operators have relied on physical references set by surveyors at a job site when operating equipment of this type, automatic machine control systems have also been developed that provide an optical reference, such as a reference beam of laser light, to specify elevation. In such a system, a laser receiver mounted on the grader senses the laser beam and provides an elevation reference. The sensed elevation of the reference laser beam is compared to a set point, either by a machine operator or by an automatic control. The movement of the machine element is then controlled based on this information, either manually by an operator or automatically by an automated control. The set point, that is, the desired vertical position, may be adjusted depending upon the x and y location of the machine at the work site, with this machine location being determined in any of a number of ways.
Total stations have been used both for surveying and for machine control. In a typical surveying application, a total station, positioned at a known location, directs a beam of laser light to a target positioned by a surveyor at a point to be surveyed. The target includes retroreflectors which reflect the beam back to the total station. By measuring the time of flight of the beam, the distance between the total station and the target is determined. By also measuring the direction of the beam from the total station to the target, i.e., the altitude and azimuth angles that define a vector from the total station to the target, the location of the target is precisely determined.
Robotic total stations have been developed that are capable of locating and tracking a target without being attended by an operator. With a robotic total station, the surveyor moves the target around the work site. Servo motors in the robotic total station cause it to rotate toward the target, providing precise angular and distance measurements as the surveyor moves to various locations at the work site. The total station automatically tracks the remote target as it moves, thus providing real-time position data for the target.
Robotic total stations have also been used for machine control. They typically use a single robotic station with single target per machine. The position information is communicated to the machine control system remotely where the control software calculates the machine element position relative to the job plan. Multiple targets on a single machine element have required multiple robotic stations. Such arrangements have been somewhat complicated. There is, therefore, a need for a simplified system using a single total station.